Determining the characteristic reading distance of an individual is very important for making ophthalmic lenses that provide their wearer with optical correction that is personalized and in particular that is adapted to the individual's near vision.
Document JP 2000-325309 discloses a device for determining such a characteristic distance and that comprises firstly a reading medium implemented in the form of a tablet placed at a distance suitable for reading text carried by said tablet, and secondly measurement means for measuring the distance of the head relative to the tablet. Those distance measurement means make use of ultrasound: an ultrasound emitter and an ultrasound receiver are provided on the tablet. The receiver detects the ultrasound that has been emitted by the emitter and reflected on the individual's head. That method presents the drawback of not being very accurate.